The advent of modern power tools has allowed many material removal and material forming processes that were typically performed by hand to be performed with greater efficiency, greater precision and typically at a lower cost. The modern power tool is typically comprised of three main systems, the power system, the tool system and a safety system. The power system transfers a first energy type to a second energy type that the tool system is able to use. The tool system performs the material removal or material forming processes using the energy from the power system. Lastly, the safety system prevents dangerous conditions between the tool system and the operator of the power tool.
Many devices utilize power systems to convert an energy source into a useable form. In modern power tools, the power systems typically convert either hydrocarbon based fuels or electrical energy into mechanical energy. Hydrocarbon fuel power systems are normally on such devices as chain saws and trimmers; whereas electrical power systems are found on such devices as drills and table saws.
In many instances, the tool system of a power tool resembles the hand tool that was originally utilized to perform wood working operations. For example, a hand drill and a power drill both utilize a drill bit to remove material in a circular shape from a workpiece. In other instances, modern power tools utilize tool systems that are unique. For example, a circular saw utilizes a circular shaped saw blade having a plurality of teeth disposed around the circumference of the blade. While the teeth of the circular saw blade are similar to the ones formed on a hand saw, the circular configuration on the blade facilitates rotational motion of the blade as it engages a workpiece.
Since many of the safety systems set forth herein are described in relation to either a table saw or a miter saw, each of these power tools are further described below. A typical table saw generally includes a base that supports a generally flat table top having a longitudinally extending throat slot or opening through which a saw blade or other cutting tool protrudes above the table for engaging a workpiece. A motor is mounted beneath the table top, and the cutting tool, typically a circular saw blade, is mounted for rotation to the output shaft of the motor. The saw blade is positioned to effect cutting of the workpiece as it is moved longitudinally along the table. The saw blade can be lowered or raised with respect to the table top to accommodate workpieces of varying thicknesses as well as adjusted to various angular orientations relative to the plane of the table top in order to cut bevels or other such angular cuts on the workpiece.
Additionally, a typical miter saw generally includes a base member having a slot formed therethrough for receiving a saw blade and a pivotal support arm coupled to the base member. A saw is mounted to the distal end of the support arm. When the arm is lowered, the saw blade engages the workpiece, thereby cutting the workpiece. Additionally, the miter saw may include a mechanism for rotating the support arm around a z-axis (upward) relative to the base member for performing angled cutting operations.
Various safety systems have been developed to minimize the risk of injury during the operation of such power tools. Exemplary power tool safety systems may include guard mechanisms and operator detection systems. A guard physically prevents the operator from making physical contact with the active portions of the tool, such as belts, shafts, blades, etc. However, some power tools preclude the use of a guard that would effectively prevent the operator from making contact with the active portion of the tool. In these instances, operator detection systems have been developed to prevent and/or reduce injurious contact between the operator and the active portion of the power tool.
A conventional operator detection system for a power tool is generally comprised of three primary subsystems: a detection subsystem, a control subsystem and a reaction subsystem. The detection subsystem or sensing mechanism tracks the proximity of the operator in relation to the active portion of the power tool. The control subsystem determines the appropriate response to input received from the detection subsystem. Lastly, the reaction system or safety mechanism may initiate a protective operation, if applicable, that prevents and/or reduces potentially injurious contact between the operator and the active portion of the power tool. Each of these subsystems are further described below.
Detection subsystems operatively determine the location of the operator's body to the active portion of the power tool. Three known types of detection means are currently employed. First, fixed detection subsystems utilize various sensing techniques to determine if a particular portion of an operator's body is located in a certain position proximate to the power. For example, a trigger mechanism may be located on the handle portion of a miter saw. The trigger mechanism ensures that the power tool is only operated when the operator's hand is grasping the handle. If the operator's hand does not engage the trigger mechanism, the power tool will not operate, thereby preventing injury to the operator of power tool. If the trigger is disengaged when the power tool is operating, the trigger mechanism may cut power to the active portion of the tool.
Second, proximate detection subsystems utilize various sensing techniques to determine the proximity of the operator to the active portion of the power tool. In one known approach, an electrical signal is transmitted through the active portion of the power tool. A receiver is coupled to the operator's body to receive the signal. When the active portion of the power tool is brought in close proximity to the receiver, the received signal is increased. As the intensity of the received signal increases, the control system determines if the signal intensity exceeds some predetermined threshold level. If so, the control subsystem may initiate some protective operation to prevent and/or reduce operator injury.
Third, contact detection subsystems generally employ various capacitive sensing techniques to determine when the operator physically touches the active portion of the power tool. In one known approach, an electrical signal is transmitted from a transmitter to a receiver, where the transmitter is capacitively coupled via the active portion of the tool to the receiver. When the operator touches the active portion, there is a sudden decrease in the signal level detected at the receiver. Accordingly, if the sensed signal level drops below some predetermined threshold level, the control subsystem may initiate some protective operation to prevent and/or reduce operator injury.
Control subsystems determine an appropriate response to input received from the detection subsystem. When the control system determines that the operator's body is in dangerous proximity to the active portion of the power tool, it may initiate some protective operation to prevent and/or reduce operator injury.
The control subsystem may then interact, if applicable, with the reaction subsystem to carry out a protective operation that prevents and/or reduces potentially injurious contact between the operator and the active portion of the power tool. The reaction system may prevent and/or reduce the potential of operator injury in one of a variety of ways. For example, a braking mechanism may be employed to slow or stop movement of the active portion of the tool. Alternatively, an active retraction mechanisms may operatively moves the active portion of the tool away from of the operator's body, thereby prevent injurious contact.
The present application sets forth numerous improved safety mechanisms for preventing and/or reducing potentially injurious contact between an operator and active portion of a power tool. At least one known safety system for power tools is set forth in International Publication No. WO 01/26064 which is incorporated by reference herein. It is to be understood that the safety mechanisms set forth below may be integrated with this exemplary safety system and/or other known power tool safety systems. For a more complete understanding of the present invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.